Lens array and image display device incorporating the same

ABSTRACT

An image display device includes a light source, an imaging element to form an image with a light beam from the light source, and a lens array illuminated with the light beam forming the image for image display, in which lenses are arranged closely to each other. In which in the lens array a curvature radius of a surface of a border of neighboring lenses is set to be smaller than a wavelength of the light beam.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from JapanesePatent Application No. 2012-279736, filed on Dec. 21, 2012 and No.2013-221274, filed on Oct. 24, 2013.

TECHNICAL FIELD

The present invention relates to a lens array and an image displaydevice incorporating the lens array.

BACKGROUND ART

The image display device can be incorporated as a headup display devicein various kinds of an operable vehicle such as automobile, train, shipand vessel, helicopter, airplane.

Japanese Patent Application Publication No. 2009-128659 (Reference 1)and No. 2010-145745 (Reference 2) disclose a headup display device as animage display device which two-dimensionally scans alight beam todisplay an image.

This device includes a deflector to two-dimensionally deflect a lightbeam modulated in intensity by an image signal and scans a micro lensarray with the deflected light beam to form an image thereon. The imageis enlarged by a virtual image optical system and formed as an enlargedvirtual image.

A reflective element is provided prior to the position of the enlargedvirtual image to reflect the image to an observation side forobservation.

A laser beam with high optical energy density and directivity issuitable for the light beam forming the image, as described inReferences 1 and 2.

However, due to the coherence of a laser beam, interfering noise such asspeckle is likely to occur in an observed image. Interference fringesare a typical example of interfering noise. Interference fringes bringabout degradation of image quality and visibility.

Reference 1 discloses an interfering noise removing method. Therein,micro convex cylindrical lenses are arranged as a micro lens array andthe beam diameter of a scanning coherent light beam is set to a smallervalue than a pitch with which the micro lenses are arranged. Then, alight source is configured to emit a light beam in pulse insynchronization with scanning so that the light beam is irradiated notastride border portions of neighboring micro lenses but only on themicro lenses.

Alternatively, an optical shield layer can be provided on the borderportions in order to block the light beam from irradiating the borderportions.

Interfering noise can be effectively removed in the above manners.However, to emit the light beam in pulse in synchronization withscanning and illuminate only the micro lenses, a light source and aportion scanning the light beam need to have a complex structure.

Further, with the shield layer formed at the borders, a light beam canbe continuously scanned, however, the light blocking by the shield layermay result in a decrease in the brightness of a displayed enlargedvirtual image.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an image display devicewhich can effectively reduce visible interfering noise while maintainingthe brightness of an enlarged virtual image displayed by two-dimensionalscanning with a coherent light beam.

According to one embodiment, an image display device comprises a lightsource, an imaging element to form an image with a light beam from thelight source, and a lens array illuminated with the light beam formingthe image for image display, in which lenses are arranged closely toeach other, wherein in the lens array a curvature radius of a surface ofa border of neighboring lenses is set to be smaller than a wavelength ofthe light beam.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, embodiments, and advantages of the present invention willbecome apparent from the following detailed description with referenceto the accompanying drawings:

FIGS. 1A to 1C show an image display device according to one embodimentof the present invention;

FIGS. 2A, 2B show the divergence of light by a micro convex lens andoccurrence of interfering noise;

FIGS. 3A to 3C show how to remove interfering noise;

FIGS. 4A to 4C show three examples of how micro convex lenses arearranged;

FIGS. 5A to 5E show five other examples of how micro convex lenses arearranged;

FIG. 6 shows an anamorphic micro convex lens; and

FIGS. 7A, 7B show two examples of a micro lens array.

DESCRIPTION OF EMBODIMENT

Hereinafter, an embodiment of an image display device will be describedin detail with reference to the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

FIGS. 1A to 1C show one example of an image display device according tothe present embodiment.

The image display device is a headup display device to displaytwo-dimensional color images. FIG. 1A shows the overall structure of thedevice.

In FIG. 1A the image display device comprises a light source 100, anoptical deflector 6, concave mirrors 7, 9, a micro lens array 8, and areflective element 10.

The light source 100 projects a light beam LC for color image display.The light beam LC is a light beam formed by combining red (R), green(G), and blue (B) color beams into one.

The structure of the light source 100 is shown in FIG. 1B by way ofexample. The light source 100 includes semiconductor lasers RS, GS, BSto emit RGB laser beams, respectively, coupling lenses RCP, GCP, BCP toreduce the divergence of the three-color laser beams from thesemiconductor lasers RS, GS, BS, apertures RAP, GAP, BAP to limit thebeam diameters of the color laser beams, a beam synthesizing prism 101,and a lens 102.

The color laser beams of the adjusted beam diameter are incident on thebeam synthesizing prism 101 which includes a dichroic film D1 totransmit red light therethrough and reflect green light, and a dichroicfilm D2 to transmit the red and green light therethrough and reflectblue light. Thereby, the beam synthesizing prism 101 combines red,green, and blue laser beams into a single laser beam for projection.

The single laser beam is then converted to a parallel laser beam with acertain diameter by the lens 102. The parallel laser beam is the lightbeam LC for image display.

The RGB laser beams constituting the light beam LC are modulated inintensity by an image signal of a color image to be displayed. That is,the semiconductor lasers RS, GS, BS are modulated in emission intensityby a not-shown driver in accordance with the respective image signals ofRGB components.

The light beam LC from the light source 100 is incident on the opticaldeflector 6 as an imaging element and two-dimensionally deflectedthereby. According to the present embodiment the optical deflector 6 iscomprised of a micro mirror to oscillate around two mutuallyperpendicular axes.

Specifically, the optical deflector 6 is a MEMS (Micro ElectroMechanical System) mirror manufactured by a semiconductor process or thelike.

Alternatively, the optical deflector 6 can be configured of two micromirrors each oscillating around an axis, to oscillate in two mutuallyperpendicular directions.

The deflected light beam LC is incident on the concave mirror 7 andreflected to the micro lens array 8.

The concave mirror 7 functions to reflect the incident light beam LC ina constant direction. Thus, the light beam LC from the concave mirror 7travels in parallel along with the deflection of the optical deflector 6to the micro lens array 8 and two-dimensionally scans the micro lensarray 8.

A two-dimensional color image is formed on the micro lens array 8 by thescanning. Needless to say that only the pixel illuminated with the lightbeam LC at each instant is displayed at the instant.

The color image is formed as an aggregate of pixels displayed at eachinstant by the scanning with the light beam LC. The light forming thecolor image on the micro lens array 8 is incident on and reflected bythe concave mirror 9.

Although not shown in FIGS. 1A to 1C, the micro lens array 8 has alater-described micro convex lens structure. The concave mirror 9constitutes a virtual image optical system.

The virtual image optical system forms an enlarged virtual image 12 ofthe color image. The reflective element 10 is provided prior to theposition of the enlarged virtual image 12 to reflect the light formingthe enlarged virtual image 12 to an observer 11 as represented by theeye in the drawing. By the reflected light the observer 11 can see theenlarged virtual image 12.

Note that in FIG. 1A vertical direction is defined as Y direction whiledirection orthogonal to the drawing is defined as X direction. Herein, Ydirection is also referred to as longitudinal direction and X directionis referred to as transverse direction.

In the micro lens array 8 the micro convex lenses are tightly arrangedwith a pitch close to a pixel pitch. Each micro convex lens includes afunction to diverge the light beam LC, as described in the following.

FIG. 1C shows four light beams L1 to L4 to be incident on the micro lensarray 8. It is assumed that the light beams L1 to L4 be incident on thefour corners of the image on the micro lens array 8.

Having transmitted through the micro lens array 8, the light beams L1 toL4 are converted to light beams L11 to L14.

If the light with a cross section of a quadrangle shape surrounded bythe light beams L1 to L4 is incident on the micro lens array 8, thelight is converted to a divergent light surrounded by the light beamsL11 to L14. In reality the light beam LC is incident on a specific microconvex lens of the micro lens array 8 at some instant and convertedthereby to a divergent beam.

Thus, each micro convex lens diverges the light beam. The divergent beamsurrounded by the light beams L1 to L4 is a result of collecting thediverged light beam LC temporally. The light beam LC is diverged for thepurpose of irradiating a wide area in the vicinity of the observer 11'seyes with the light beam reflected by the reflective element 10.

Without the optical divergence, the area which the light beam reflectedby the reflective element 10 irradiates is limited to only a small areanear the observer 11's eyes. If the observer 11 moves his/her head,his/her eyes positions deviate from the small area, the observer 11cannot view the enlarged virtual image 12.

As described above, the diverged light beam LC can irradiate a wide areanear the observer 11's eyes, which allows the observer to surely viewthe enlarged virtual image 12 irrelevant of a small motion of the head.

Thus, according to the present embodiment the light beam is a parallelbeam when incident on the micro lens array 8 and converted to adivergent beam after transmitting through the micro lens array 8.

Next, the micro convex lenses of the micro lens array 8 are describedwith reference to FIG. 2A, 2B and FIGS. 3A to 3C.

Each micro convex lens is configured to be larger in diameter than thebeam diameter of the light beam LC in order to reduce interfering noise.

FIG. 2A shows a micro lens array 802 in which micro convex lenses 801are densely arranged. The diameter 806 of the micro convex lens 801 islarger than the beam diameter 807 of a light beam 803.

According to the present embodiment the light beam 803 is a laser beamand exhibits an optical intensity distribution around the beam centersimilar to a Gaussian distribution. Accordingly, the beam diameter 807is a distance along a beam radius in which optical intensity decreasesto 1/e² in the optical intensity distribution. In FIG. 2A the beamdiameter 807 appears equal to the diameter of the micro convex lens 801but it does not need to be equal thereto. It has only not to protrudefrom the micro convex lens 801.

In FIG. 2A the entire light beam is incident on a single micro convexlens 801 and converted thereby to a divergent beam 804 at a divergentangle 805. In this case interfering noise will not occur since there isonly one divergent beam 804 and no interfering beams.

Note that the magnitude of the divergent angle 805 can be arbitrarilyset in accordance with the shape of the micro convex lens 801.

In FIG. 2B the beam diameter of a light beam 811 is double the pitch 812at which micro convex lenses are arranged. The light beam 811 isincident over two micro convex lenses 813, 814.

In this case the light beam 811 is diverged by the micro convex lenses813, 814 to two divergent beams 815, 816. The divergent beams 815, 816then overlap and interfere with each other in an area 817 andinterfering noise occurs in this area.

Further, in FIG. 3A a light beam 824 is incident over two micro convexlenses 822, 823 of a micro lens array 821. The beam diameter of thelight beam 824 is equal to the diameter of each micro convex lens. Inthis case one portion of the beam 824 incident on the micro convex lens822 is converted to a divergent beam 826 while the other portionincident on the micro convex lens 823 is converted to a divergent beam827.

Thus, the divergent beams 826 and 827 are diverged to separate away fromeach other and do not overlap so that interfering noise will not occur.

As described above, the interfering noise arising from the beamsdiverged by the micro convex lenses can be prevented when the beamdiameter of the light beam 824 is set to be equal to or less than thediameter of the micro convex lens 822.

Next, the numeric examples of the diameter of the micro convex lens andthe beam diameter of the light beam are described.

The diameter of the light beam for image display is easily set to about150 μm, for example. The diameter of each micro convex lens is then setto be larger than 150 μm, for example, 160 μm, 200 μm.

In FIG. 3A the micro convex lenses 822, 823 . . . of the micro lensarray 821 are arranged without a gap. The width of a border between twoneighboring micro convex lenses should be zero. Only the divergent beams826, 827 are generated from the incident light beam 824.

However, in actual micro convex lens structure as a micro lens array 831the width of a border 835 between neighboring micro convex lenses 833,834 cannot be zero, as shown in FIG. 3B. Microscopically, the edges ofthe two neighboring micro convex lenses are smoothly continued, forminga curved surface at the border 835. This curved surface acts as a microlens surface to an incident light beam.

Therefore, a divergent beam 838 in addition to the divergent beams 836,837 occurs from the light beam 832 incident astride the border 835 ofthe micro convex lenses 833, 834, and overlaps with the divergent beams836, 837 in areas 839, 840, causing interfering noise.

FIG. 3C shows how to abate or prevent interfering noise in the microconvex lens structure.

The curved surface of a border 843 gradually connecting the surfaces ofmicro convex lens 841, 842 acts as a micro lens surface. The curvatureradius of the curved surface is set to r.

Herein, the light beam incident on the micro convex lens structure isassumed to be a single color laser beam with a wavelength λ for the sakeof simplicity. When the curvature radius r of the border 843 is largerthan the wavelength λ of the laser beam (r>λ), the curved surface exertslens effects on an incident laser beam. Then, a beam component passingthrough the border 843 is diverged and overlaps with the divergent beamsfrom the micro convex lenses 841, 842, causing interfering noise.

Meanwhile, when the curvature radius r of the border 843 is smaller thanthe wavelength λ of the laser beam (r<λ), the border 843 becomes asub-wavelength structure to the laser beam. It is well known that asub-wavelength structure does not exert lens effects on light with awavelength larger than the sub-wavelength structure. Thus, the border843 with a curvature radius r smaller than the wavelength λ does notfunction as a lens and has the light beam transmit straight therethroughand not diverged.

Accordingly, a beam portion having transmitted straight through theborder 843 does not overlap with the divergent beams from the microconvex lenses 841, 842 and does not cause interfering noise.

Specifically, it is preferable to set a relation of magnitude among thediameter d of the light beam, wavelength λ, diameter D of the microconvex lens, and curvature radius r of a border surface, as follows:D>d,λ>r

To display a monochrome enlarged virtual image, the light beam is formedof single-color coherent light with a wavelength λ. Then, the aboveparameters d, λ, D, r are set to satisfy the relation of magnitudeabove. Thereby, interfering noise can be reduced.

According to the present embodiment the light beam LC is a combined RGBlight beam for display of color images. The relation of magnitude amongthe wavelengths λR (640 nm), λG (510 nm), λB (445 nm) of the three beamsis such that λR>λG>λB.

In view of preventing the occurrence of interfering noise, the curvatureradius r of the border surface should be set to 400 nm smaller than theshortest wavelength λB, for example. Moreover, with the curvature radiusr smaller than the longest wavelength λR, for example, 600 nm, theinterfering noise caused by the R components of the light beam can beprevented. The interfering noise can be effectively reduced.

When the curvature radius r is set to, for example, 500 nm so that r<λG,the interfering noise caused by the R and G components of the light beamcan be prevented. Interfering noise occurs from three RGB components ofthe light beam LC independently and the independent interfering noisefrom the RGB components is collectively recognized visibly by theobserver. Therefore, such visible interfering noise can be greatlyreduced by eliminating interfering noise caused by one color, the Rcomponents with the longest wavelength only, contributing to improvingthe quality of an image to be observed. Noise reduction effects arefurther improved by eliminating the interfering noise caused by the Gcomponents and B components in this order. Thus, setting the curvatureradius to 600 nm, for example, smaller than the longest wavelength λRmakes it possible to achieve a decrease in interfering noise in acertain level.

In general the relation, R≈G>B holds true in terms of the visibility ofinterfering noise although the intensity of the interfering noise variesdepending on wavelength, beam diameter, and multiple/single mode. Thatis, the visibility of the human eyes is low to light with a wavelengthλB, therefore, interfering noise is not conspicuous. With the curvatureradius r set to, for example, 500 nm, smaller than the wavelength λG,highly visible interfering noise caused by light with the wavelengthsλR, λG can be reduced. With the curvature radius r set to, for example,400 nm smaller than the wavelength λB, the interfering noise can be moreeffectively reduced, as described above.

The size of each micro convex lens is in the order of 100 μm, and it isa general micro lens. The micro convex lens structure is a general microlens array.

To manufacture the micro lens array, generally, a mold having thetransfer surface of a micro lens array surface is prepared, and then themold surface is transferred onto a resin material. It is known that thetransfer surface of the mold is formed by cutting or photolithography.

Alternatively, the transfer surface can be transferred to a resinmaterial by injection molding, for example.

To reduce the curvature radius of the border of neighboring microlenses, the width of the border has to be reduced. The reduction of theborder width can be realized by sharpening the border.

There are various known techniques for manufacturing the micro lensarray mold by which the border width between neighboring micro lenses isdecreased to the order of wavelength.

For instance, Japanese Patent No. 4200223 discloses a technique toincrease the curvature radius of each micro lens by anisotropic etchingor ion process and remove a non-lens portion of a border portion.

Moreover, Japanese Patent No. 5010445 discloses a technique to remove aflat surface between neighboring micro lenses by isotropic dry etching.

By these known techniques a micro lens array having border surfaces witha sufficiently small curvature radius can be manufactured. By the microlens array with border surfaces having curvature radius less than 640nm, interfering noise due to R components can be prevented fromoccurring. Similarly, by the micro lens array with border surfaceshaving curvature radius less than 510 nm, interfering noise due to RGcomponents can be prevented from occurring. By the micro lens array withborder surfaces having curvature radius less than 445 nm, interferingnoise due to RGB components can be prevented from occurring.

The image display device as described above comprises the light source,the imaging element to form an image with a light beam from the lightsource, and the micro lens array illuminated with the light beam formingthe image for image display, in which the micro lenses are arrangedclosely to each other. In the micro lens array the curvature radius r ofthe surface of a border of neighboring micro lenses is set to be smallerthan the wavelength λ of the light beam. The concave mirror 7 in FIG. 1Ais configured to reflect the light beam LC two-dimensionally deflectedto travel in a certain direction. The concave mirror 7 functions as adeflection restrictor to adjust a deflection area of the light beam andlimit the scan area of the micro lens array.

Such a deflection restrictor is omissible if the deflection angle of thelight beam two-dimensionally deflected by the optical deflector is notlarge.

Next, examples of the arrangement of micro lenses in the micro lensarray are described.

The condition for the micro lens array and micro lenses is such thatmicro convex lenses with a diameter larger than a beam diameter of thelight beam are arranged tightly with a pitch close to a pixel pitch.Upon satisfaction of the condition, the arrangement of micro lenses canbe arbitrarily decided.

FIGS. 4A to 4C show three examples of the arrangement of micro lenses.In FIG. 4A in a micro lens array 87 square-shape micro lenses 8711,8712, . . . are arranged in square matrix.

The number of pixels of an image or an enlarged virtual image displayedwith the headup display device is determined by the pitch of the microlenses arranged in the micro lens array.

In FIG. 4A a distance between the centers of the adjacent micro lensesin X direction is set to X1 while that in Y direction is set to Y1. X1and Y1 are the pixel size of one pixel, that is, effective pixel pitch.

In FIG. 4B in a micro lens array 88 regular hexagonal micro lenses 8811,8821 . . . are densely arranged. In this arrangement each micro lensdoes not include a side parallel to X direction. The top and bottomsides of each micro lens are in a zigzag form so that this arrangementis called zigzag arrangement.

In FIG. 4C in a micro lens array 89 regular hexagonal micro lenses 8911,8921 . . . are densely arranged. In this arrangement each micro lens hassides parallel to X direction. This arrangement is called armchairarrangement and the zigzag arrangement and armchair arrangement arecollectively called honeycomb arrangement.

The armchair arrangement in FIG. 4C is formed by rotating the zigzagarrangement in FIG. 4B by 90 degrees. In the zigzag arrangementeffective pixel pitches in X and Y directions are X2 and Y2,respectively.

In the armchair arrangement effective pixel pitches in X and Ydirections are X3 and Y3, respectively.

In FIG. 4B the effective pixel pitch Y2 is a distance between the centerof the micro lens 8821 and the midpoint of the right side of the microlens 8811.

In FIG. 4C the effective pixel pitch X3 is a distance between the centerof the micro lens 8911 and the midpoint of a common side of two microlenses contacting the right sides of the micro lens 8911.

In the zigzag arrangement the effective pixel pitch X2 is small so thata resolution of an image display can be improved in X direction.Similarly, in the armchair arrangement an image resolution can beimproved in Y direction.

By the micro lens array in the honeycomb arrangement, it is possible toeffectively represent a pixel of size smaller than an actual lensdiameter and increase the effective pixel number.

Further, as described above, the borders of neighboring micro lenses canbe, for example, formed to have the curvature radius r smaller than thewavelength λR of the R components of the light beam LC in order toprevent interfering noise due to R components of coherent light.

However, if the curvature radius is larger than the wavelengths λG, λBof the G and B components, these lights will be diverged by the borderportions and interfere with each other, causing interfering noise.

In such a case, in the square matrix arrangement in FIG. 4A the lightbeam is diverged at the borders in both Ya and Xa directions, causinginterfering noise.

Meanwhile, in the honeycomb arrangement in FIGS. 4B and 4C the lightbeam is diverged at the borders in three directions 8A, 8B, 8C and 9A,9B, 9C, respectively.

Thus, in the square matrix arrangement interfering noise occursbi-directionally while in the honeycomb arrangement it occurstri-directionally.

Since the maximal intensity of coherent light causing interfering noiseis constant, the larger the number of diverged lights, the weaker thecontrast of interfering noise and the less visible or conspicuous itbecomes. Therefore, the micro lens array is preferably arranged inhoneycomb form when interfering noise caused by wavelength componentssmaller than the curvature radius r of the border portion is allowed.

As described above, referring to FIG. 1A, the virtual image opticalsystem is comprised of the concave mirror 9 to form the enlarged virtualimage 12. That is, the enlarged virtual image 12 is an aggregate ofenlarged pixel images formed by the concave mirror 9.

By forming each micro lens as anamorphic lens, the micro lens candiverge the light beam in two mutually perpendicular directions.

FIG. 6 shows elliptic micro lenses 80 of the micro lens array 8. Thesize of a border between micro lenses is not taken into consideration inthe drawing. In FIG. 6 the power of the micro lenses 80 is larger in Xdirection than in Y direction, in other words, the curvature of themicro lenses is larger in X direction than in Y direction.

As shown in the drawing, the light beam LC incident on and diverged byeach micro lens 80 will have an elliptic cross section FX, long in Xdirection. Thus, the divergent angle of each light beam is larger in Xdirection than in Y direction.

That is, as seen from the observer 11, the view angle of the enlargedvirtual image 12 is larger in X direction, and in FIG. 6 the microlenses are long in Y direction. The shape of the micro lenses can be anoblong hexagon long in X direction, as shown in FIG. 5B. In this casewhen the power of a micro lens 9211 is larger in X direction than Ydirection, the cross section FX of a divergent beam from the micro lenswill be a wide hexagon long in X direction.

The above headup display device can be mounted in an automobile, forexample, to allow a driver to view the enlarged virtual image whiledriving. In automobile, X direction is a transverse direction and Ydirection is a longitudinal direction when seen from a driver's seat.The windshield of an automobile functions as the reflective element 10.

The enlarged virtual image 12 can be displayed as a navigation image infront of the windshield, for example. A driver or the observer 11 canview the image from the driver's seat.

In general the enlarged virtual image has preferably a larger angle ofview in X direction so that the driver can surely see the image even ifhe/she moves the eyes in X direction.

Further, a larger view angle is required in transverse direction than inlongitudinal direction so that the driver can see the display diagonallyfrom right and left sides. Accordingly, the micro lenses are required toexhibit a larger divergent angle (non-isotropic diffusion) inlongitudinal or X direction than in transverse or Y direction of theenlarged virtual image.

Thus, it is preferable that the micro convex lenses of the micro lensarray are formed as anamorphic lenses, and the divergent angle of thelight beam LC is larger in transverse direction than in longitudinaldirection of the enlarged virtual image.

Thereby, the micro lens array can diverge the light beam in a requiredminimal angle range satisfying the necessary angle of view of the headupdisplay device, contributing to improving optical use efficiency andbrightness of a displayed image.

Alternatively, the micro lens array can be configured to exhibitisotropic diffusion at the same divergent angle longitudinally andtransversely, instead of non-isotropic diffusion.

Moreover, it is known that the surfaces of the micro convex lenses canbe formed as aspheric. The anamorphic lens surface according to thepresent embodiment is also aspheric, and it can be formed as a moregeneral type aspheric surface to correct aberration. By aberrationcorrection, unevenness in the intensity of optical divergence can bereduced.

In FIGS. 4A to 4C the square or regular hexagonal-shape micro convexlenses are shown by way of example. The shape of the micro convex lensesshould not be limited to such examples. It can be shaped such that theshapes shown in FIGS. 4A to 4C are extended in one direction. That is,the square is turned into a rectangle and the regular hexagon is turnedinto a deformed long hexagon.

In FIGS. 4A to 4C the effective pixel pitches of the micro lens array inX and Y directions are X1 to X3 and Y1 to Y3, respectively. The ratiobetween the effective pixel pitches in X and Y directions SX, SY iscalled aspect ratio SY/SX.

In FIG. 4A since X1=Y1, the aspect ratio. Y1/X1 is 1.0

In FIG. 4B since Y2>X2, the aspect ratio Y2/X2 is larger than 1.0

In FIG. 4C since Y3<X3, the aspect ratio Y3/X3 is smaller than 1.0

FIGS. 5A to 5E show other examples of the arrangement of micro convexlenses. The effective pixel pitches in X and Y directions are X11, Y11,X12, Y12, and X13, Y13.

In FIG. 5A in a micro lens array 91 rectangular micro convex lenses9111, 9112 . . . , 9121 . . . are arranged in square matrix and theaspect ratio is larger than 1.0.

In FIG. 5B to 5E in micro lens arrays 92 to 95 micro convex lenses arearranged in honeycomb form and the aspect ratios thereof Y12/X12,Y13/X13 are both larger than 1.0.

The five examples of micro lens array are all larger in length in Ydirection than in X direction. This type of micro convex lenses can beeasily formed to have a larger curvature in X direction than in Ydirection. Accordingly, they can easily realize anamorphic effects toexert larger optical power in X direction than in Y direction.

For example, in FIG. 5A the effective pixel pitches are set to X11=150μm and Y11=200 μm, and the aspect ratio will be 200/150=4/3>1. Also, thebeam diameter of the light beam needs to be smaller than 150 μm.

In the micro lens arrays in honeycomb form in FIGS. 5B to 5E the shapeof each micro convex lens is long in Y direction. Specifically, themicro lens array in FIG. 5B is of the zigzag type and those in FIGS. 5Cto 5E are of the armchair type.

The zigzag type honeycomb arrangement in FIG. 5B and armchair typehoneycomb arrangement in FIG. 5C are both useful. However, thearrangement in FIG. 5C is more advantageous than that in FIG. 5B becausea difference in the longitudinal and transverse lengths of the microconvex lens and a difference between the longitudinal and transverseeffective pixel pitches are both smaller.

Specifically, in FIG. 5B assumed that the diameter R2 x of each microconvex lens 9211, 9212, . . . in X direction is 100 μm and that R2 y inY direction is 200 μm. Then, the effective pixel pitch X12 in Xdirection is 50 μm and that Y12 in Y direction is 150 μm.

Similarly, in FIG. 5C assumed that the lens diameter R3 x of each microconvex lens 9311, 9312, . . . in X direction is 100 μm and that R3 y inY direction is 200 μm. Then, the effective pixel pitch X13 in Xdirection is 75 μm and that Y13 in Y direction is 100 μm.

Thus, the differences in the effective pixel pitches in X and Ydirections are smaller in FIG. 5C (50 μm and 75 μm) than in FIG. 5B (50μm and 100 μm).

In the honeycomb type arrangements in FIGS. 5C to 5E the transverse andlongitudinal effective pixel pitches are all defined as X13 and Y13. InFIGS. 5D, 5E the top and bottom sides of each micro convex lens parallelto X direction are longer than oblique sides.

In FIGS. 5D, 5E the effective pixel pitches X13, Y13 can be equalizedowing to the vertically long structure. Further, the shape of each microconvex lens can be arbitrarily decided for the purpose of controllingthe divergent angle of a diverged light beam. The lengths of the sidesof the oblong hexagon can be arbitrary.

Thus, the armchair type honeycomb arrangement can improve the brightnessof an image and the effective pixel number and reduce the difference inthe effective pixel pitches in X and Y directions.

In the headup display device in FIG. 1A the light beam LC is incident onthe micro lens array 8 orthogonally. However, the light beam LC is notalways orthogonally incident thereon.

For example, in order to downsize the headup display device by changingthe arrangement of the optical elements from the light source to thereflective element, the light beam LC can be incident on the micro lensarray 8, as shown in FIGS. 7A, 7B.

In FIG. 7A the incidence angle of the light beam LC is inclined relativeto the micro lens array 8.

With use of the micro convex lens having an aspheric surface, the lightbeam LC is incident obliquely relative to the optical axis of theaspheric surface. Therefore, the effects of the aspheric surface may notbe exerted.

In such a case, preferably, in a micro lens array 8 a micro convexlenses ML are placed so that their optical axes AX are inclined relativeto a direction orthogonal to the reference surface of the micro lensarray 8 a, as shown in FIG. 7B. Thereby, the optical axes AX areparallel or approximately parallel to the incidence direction of thelight beam LC. Note that the reference surface is a surface on which themicro convex lenses ML are arranged.

Thus, it is made possible to downsize the optical system, improveoptical use efficiency and stably diverge the light beam LC in aconstant direction.

The headup display device according to the present embodiment can beincorporated in various kinds of operable vehicles such as train, shipand vessel, helicopter, airplane in addition to the automobile describedabove. In such a case a glass element ahead of an operator's seat can bea reflective element.

Further, the headup display device according to the present embodimentcan be implemented as a two-dimensional image display device for movies,for instance.

Further, the micro convex lenses can be configured to diverge the lightbeam in one direction only instead of two directions X, Y. In such acase the lens surfaces thereof can be formed as a micro convex cylindersurface.

According to the present embodiment, the image display device canimprove optical use efficiency and the brightness of a displayed image.In addition, by use of the micro lens array having curvature in both Xand Y directions on the lens surface, it can abate visible interferingnoise.

Although the present invention has been described in terms of exemplaryembodiments, it is not limited thereto. It should be appreciated thatvariations or modifications may be made in the embodiments described bypersons skilled in the art without departing from the scope of thepresent invention as defined by the following claims.

The invention claimed is:
 1. An image display device comprising: a lightsource which projects a light beam; an imaging element to form an imagewith the light beam from the light source; and a lens array illuminatedwith the light beam forming the image for image display, in which lensesare arranged closely to each other, wherein in the lens array acurvature radius of a surface of a border of neighboring lenses is setto be smaller than a wavelength of the light beam, the light sourceincludes two or more light sources to project light beams with differentwavelengths from each other, and the curvature radius of the surface ofthe border of neighboring lenses is set to be smaller than a longestwavelength among wavelengths of the light beams.
 2. The image displaydevice according to claim 1, wherein the imaging element is an opticaldeflector to two-dimensionally deflect the light beam from the lightsource, the image display device further comprising a deflectionrestrictor to adjust an area in which the light beam istwo-dimensionally deflected by the optical deflector and restrict a scanarea of the lens array.
 3. The image display device according to claim1, wherein lenses of the lens array are anamorphic lenses to diverge thelight beam at a wider angle in a transverse direction of the image thanin a longitudinal direction.
 4. The image display device according toclaim 1, wherein: a shape of each lens of the lens array is rectangular;and the lenses are arranged in a square matrix.
 5. The image displaydevice according to claim 4, wherein an aspect ratio of effective pixelpitches in transverse and longitudinal directions of the lenses is setto be larger than 1.0.
 6. The image display device according to claim 1,wherein a shape of each lens of the lens array is hexagonal; and thelenses are arranged in a honeycomb form.
 7. The image display deviceaccording to claim 6, wherein the honeycomb form is a zigzag form. 8.The image display device according to claim 6, wherein the honeycombform is an armchair form.
 9. The image display device according to claim1, wherein an optical axis of each lens is inclined relative to adirection orthogonal to a reference surface of the lens array.
 10. Theimage display device according to claim 1, further comprising: a virtualimage optical system to form an enlarged virtual image with the lightbeam irradiated by the lens array and; and a reflective element providedprior to a position of the enlarged virtual image to reflect the lightbeam to an observation side for image display.
 11. The image displaydevice according to claim 10, wherein the image display device is aheads up display, and when mounted in a vehicle having a glass elementin front of a driver's seat, the image display device is configured touse the glass element as the reflective element to form the enlargedvirtual image ahead of the glass element in a position viewable from thedriver's seat.
 12. The image display device according to claim 1,wherein the curvature radius of a surface of a border of neighboringlenses is set to be smaller than 640 nm.
 13. An image display deviceaccording to claim 1, wherein the curvature radius of a surface of aborder of neighboring lenses is set to be smaller than 510 nm.
 14. Animage display device according to claim 1, wherein the curvature radiusof a surface of a border of neighboring lenses is set to be smaller than445 nm.
 15. The image display device according to claim 1, wherein thelight sources include a semiconductor laser, a coupling lens, andaperture, and a beam synthesizing prism.
 16. The image display deviceaccording to claim 1, wherein a diameter of the light beams is less thanor equal to a diameter of each of the lenses of the lens array.